ST. GEORGE'S, Grenada — A Caribbean seismic research center says an underwater volcano just north of Grenada may be about to erupt but does not pose a tsunami threat to the region.

The University of the West Indies Seismic Research Center says the main threat posed by the Kick 'em Jenny submarine volcano is to shipping. All boats are being directed to observe an exclusion zone of 3.1 miles (5 kilometers) around the volcano.

The center raised its alert level Tuesday from yellow to orange amid a "substantial" increase in earthquake activity. It said an eruption may begin with less than 24-hours' notice.

The volcano is about 200 meters (660 feet) below the surface. It has erupted at least a dozen times since the 1930s but hasn't caused any known deaths or injuries.